This invention relates to a two-way clutch for selectively transmitting power, and a rotatation transmission device comprising the two-way clutch and an electromagnetic clutch for selectively engaging and disengaging the two-way clutch. The rotation transmission device is mounted e.g. on the power train of a four-wheel drive vehicle of the front-engine-rear-drive type to selectively transmit the engine power to the front wheel.
Such a two-way clutch comprises an inner ring, an outer ring and engaging elements in the form or rollers or sprags disposed between the inner and outer rings. If the engaging elements are rollers, ramps are formed on one of the inner surface of the outer ring and the outer surface of the inner ring to define wedge spaces between the inner and outer rings so that the inner and outer rings can be selectively locked and unlocked by moving the rollers into narrow and wide or neutral portions of the wedge spaces. If the engaging elements are sprags, the sprags are disposed between cylindrical surfaces of the inner and outer rings. By inclining or erecting the sprags, the inner and outer rings are selectively locked together or unlocked.
The electromagnetic clutch in the transmission device selectively engages and disengages the two-way clutch. If the rotation transmission device is used in an FR-based four-wheel drive vehicle, engine power can be selectively delivered to the front wheels by engaging the two-way clutch by activating the electromagnet of the electromagnetic clutch, as disclosed in Japanese patent publication 10-211828 filed by the applicant of the present invention.
With this arrangement, the front wheels can be cut off from the engine simply by turning off the electromagnetic clutch. Thus, tight corner braking in a part-time 4WD vehicle can be avoided simply by turning off the electromagnetic clutch while the vehicle is turning a tight corner.
Such conventional two-way clutches need rather thick inner and outer rings for sufficient rigidity and torque transmission capacity. The entire clutch is thus relatively heavy and costly.
An object of the invention is to provide a two-way clutch that has major components which can be formed by pressing, and is lightweight, less costly and high in torque transmission capacity.
Another objection of the invention is to provide a rotation transmission device including such a two-way clutch.
According to the present invention, there is provided a two-way clutch comprising a first member and a second member mounted on the first member. The first member is formed with a plurality of pockets in an outer periphery thereof, and the second member is formed with a plurality of pockets in an inner periphery thereof. A plurality of block members and a plurality of resilient members are received in the respective pockets of the first member, with the resilent members biasing the block members toward the second member. And a cam ring is provided adjacent to the second member and formed with a cam surface facing the pockets of the first member for controlling the protrusion and retraction of the block members.
According to the present invention, there is also provided a rotation transmission device comprising a first rotary member, a second rotary member, a two-way clutch, and an electromagnetic clutch having an armature and a rotor coupled to the second rotary member. The two-way clutch comprises a first member coupled to the first rotary member and a second member mounted on the first member. The first member is formed with a plurality of pockets in an outer periphery thereof, and the second member is formed with a plurality of pockets in an inner periphery thereof. A plurality of block members and a plurality of resilient members are received in the respective pockets of the first member, with the resilent members biasing the block members toward the second member. And, a cam ring is provided adjacent to the second member and formed with a cam surface facing the pockets of the first member for controlling the protrusion and retraction of the block members. The cam ring is engagable with and disengagable from the rotor in response to an external signal delivered to the electromagnetic clutch.